A projection display module and a head-mounted display device

Abstract

This invention discloses a projection display module and a head-mounted display device. The projection display module includes a light source; an optical fiber; and an optical fiber scanning device. The light input end of the optical fiber is connected to the light source, and the light output end of the optical fiber is fixed to the optical fiber scanning device. Light output from the light source is coupled into the optical fiber from the light input end and scanned out from the light output end of the optical fiber under the drive of the optical fiber scanning device. An optical fiber F-P cavity is located on the optical fiber link between the light source and the optical fiber scanning device. This solution enables more stable energy output from the semiconductor laser light source, significantly reduces noise in the optical fiber scanning display image, and improves and enhances display color, clarity, and stability.

Description

Technical Field

[0001] This invention relates to the field of projection display, and more particularly to a projection display module and a head-mounted display device. Background Technology

[0002] The imaging principle of fiber scanning display (FSD) is that the fiber scanning display device drives the optical fiber to move along a predetermined two-dimensional scanning trajectory, and modulates the light source to output the light corresponding to each pixel of the image to be displayed. Then, the light corresponding to each pixel of the image to be displayed is projected onto the projection surface one by one through the optical fiber to form a projected image.

[0003] Combining the aforementioned fiber optic scanning display technology and laser display technology modulated within an LD (Laser Diode, semiconductor laser) is considered an ideal optical display solution for AR (Augmented Reality) devices.

[0004] For semiconductor lasers, changes in environmental factors such as driving modulation, internal heat generation and temperature, as well as echoes from system links such as scattering and reflection, can cause fluctuations in the output of semiconductor lasers, such as mode skipping, energy fluctuations, wavelength drift and other problems. When the light output from the semiconductor laser is coupled and transmitted through optical fiber and then vibrated by scanning devices to display images, the above problems will lead to the inability to accurately represent the target image information, resulting in phenomena such as abnormal color, blurring and reduced contrast in the local or overall display of the system screen. Summary of the Invention

[0005] The purpose of this invention is to provide a projection display module and a head-mounted display device to solve the problems existing in the prior art, such as the inability to accurately represent target image information due to fluctuations in semiconductor laser output, resulting in abnormal colors, blurriness, and decreased contrast in the system display screen, either locally or overall.

[0006] To achieve the above-mentioned objectives, a first aspect of the present invention provides a projection display module, comprising: a light source; an optical fiber; an optical fiber scanning device; an input end of the optical fiber connected to the light source, and an output end of the optical fiber fixed to the optical fiber scanning device; light output from the light source is coupled into the optical fiber from the input end and scanned out from the output end of the optical fiber under the drive of the optical fiber scanning device; and an optical fiber FP cavity located on the optical fiber link between the light source and the optical fiber scanning device.

[0007] Optionally, an air microcavity structure can be formed inside the optical fiber by laser processing as the optical fiber FP cavity; the two end faces of the air microcavity structure are perpendicular to the axial direction of the optical fiber.

[0008] Optionally, the input fiber and the output fiber are fixed by a ring-shaped structure, with the input fiber and the output fiber spaced a certain distance apart, thereby forming a cavity between the input fiber and the output fiber as the fiber FP cavity.

[0009] Optionally, the optical fiber includes an input optical fiber, a connecting optical fiber, and an output optical fiber. The input optical fiber and the connecting optical fiber are fused together to form a first fusion splice surface, and the connecting optical fiber and the output optical fiber are fused together to form a second fusion splice surface. The optical fiber FP cavity is formed between the first fusion splice surface and the second fusion splice surface.

[0010] Optionally, the end faces of the input optical fiber and the output optical fiber are perpendicular to the axial direction of the optical fiber.

[0011] Optionally, the end faces of the input optical fiber and the output optical fiber are coated with reflective films.

[0012] Optionally, the light source includes an R, G, B tri-color laser.

[0013] A second aspect of the present invention provides a head-mounted display device, including a main body worn on a user's head, wherein at least one projection display module as described in the first aspect is disposed on the main body.

[0014] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0015] In this embodiment of the invention, a fiber optic FP cavity is provided on the fiber optic link between the light source and the fiber optic scanning device. By introducing external cavity feedback, the feedback effect increases stimulated emission of the semiconductor laser source, which can reduce the threshold current of the laser source. Due to the wavelength selectivity of the fiber optic FP cavity, the inter-mode gain and loss difference between longitudinal modes causes the originally average broadened gain line of the laser diode spectrum to saturate rapidly, thereby enhancing the suppression of adjacent modes by the preferred oscillating mode, and finally obtaining a narrowband laser output. Furthermore, by suppressing the side modes, the intensity noise and phase noise of the semiconductor laser source are reduced, thereby making the energy output of the semiconductor laser source more stable, greatly reducing the noise of the fiber optic scanning display image, and improving and enhancing the display color, clarity, and stability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort:

[0017] Figure 1 A block diagram of a projection display module provided in an embodiment of the present invention;

[0018] Figure 2A and Figure 2B The spectrum of a 520nm green semiconductor laser provided in an embodiment of the present invention;

[0019] Figure 3 A top view of an optical fiber FP cavity provided in an embodiment of the present invention;

[0020] Figure 4 A cross-sectional view of an optical fiber FP cavity provided in an embodiment of the present invention;

[0021] Figure 5 A schematic diagram of an optical fiber FP cavity provided in an embodiment of the present invention;

[0022] Figure 6 This is an optical path diagram of a beam propagating in an optical fiber FP cavity, provided in an embodiment of the present invention.

[0023] Figure 7 A schematic diagram illustrating the relationship between the power transmission coefficient and the incident light wavelength λ, provided in an embodiment of the present invention;

[0024] Figure 8 This is a schematic diagram of a pigtail light source provided in an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Please refer to Figure 1 , Figure 1 A block diagram of a projection display module provided in an embodiment of the present invention includes a light source 10; an optical fiber 11; an optical fiber scanning device 12; the light input end of the optical fiber 11 is connected to the light source 10, and the light output end of the optical fiber 11 is fixed on the optical fiber scanning device 12; the light output by the light source 10 is coupled into the light input end of the optical fiber 11 and scanned out from the light output end of the optical fiber under the drive of the optical fiber scanning device 12; and an optical fiber FP cavity 13 is located on the optical fiber link between the light source 10 and the optical fiber scanning device 12.

[0027] In this embodiment of the invention, through the wavelength selection of the fiber FP cavity and the external cavity feedback of the reflected light, the intermode gain and loss difference between multiple longitudinal modes of the semiconductor laser are changed. As a result, the originally average broadened laser gain spectrum is rapidly saturated, which enhances the suppression of similar modes by the preferential oscillating mode. Finally, a narrow-band laser output is obtained, which reduces the intensity noise and phase noise of the semiconductor laser source. This makes the energy output of the semiconductor laser source more stable, greatly reduces the noise of the fiber scanning display image, and improves and enhances the display color, clarity and stability.

[0028] In this embodiment of the invention, a 520nm green semiconductor laser is used as an example for illustration. Figure 2A and Figure 2B As shown, Figure 2A This is the spectrum of a 520nm green semiconductor laser. Figure 2B To enhance the spectral profile of the 520nm green semiconductor laser with an added fiber optic FP cavity, from... Figure 2A and Figure 2B It is evident that the original average broadened laser gain spectrum underwent rapid saturation, which enhanced the suppression of similar modes by the preferential oscillating mode, ultimately resulting in a narrow-band laser output.

[0029] In this embodiment of the invention, the following possible fiber optic FP cavity structures are described. In specific implementation, other similar fiber optic FP cavity structures may also be used, and the invention does not limit them.

[0030] In one alternative implementation, an air microcavity structure 31 can be formed on a surface perpendicular to the fiber core 30 using laser processing, thereby realizing an optical fiber FP cavity, such as... Figure 3 The image shown is a top view of the fiber optic FP cavity provided in an embodiment of the present invention.

[0031] In another alternative implementation, such as Figure 4 The diagram shown is a cross-sectional view of a fiber optic FP cavity provided in an embodiment of the present invention. The input fiber 41 and the output fiber 42 can be fixed by a ring-mounted structure 40, with a certain distance between them, thereby forming a cavity 43 between the input fiber 41 and the output fiber 42, thus realizing a fiber optic FP cavity. The cavity medium of the fiber optic FP cavity can be air.

[0032] In a third alternative implementation, at least three fiber segments can be further fused together to form a fiber FP cavity between the two fusion splice surfaces. For example... Figure 5As shown, from left to right, the optical fibers are: input fiber 50, connecting fiber 51, and output fiber 52. The input fiber 50 and connecting fiber 51 are fused together to form a first fusion surface 501, and the connecting fiber 51 and output fiber 52 are fused together to form a second fusion surface 502. The fiber optic FP cavity 53 is formed between the first fusion surface 501 and the second fusion surface 502. The internal medium of the fiber optic FP cavity 53 is optical fiber.

[0033] In this embodiment of the invention, the intracavity medium of the fiber optic FP cavity can be air, such as... Figure 3 The fiber optic FP cavity shown can also have its internal medium as the optical fiber itself, such as... Figure 5 The fiber optic FP cavity shown is illustrated. Both the input and output fiber end faces are ground and polished, with the fiber end faces perpendicular to the fiber axis. The fiber end faces may or may not be coated. If coating is applied to the fiber end faces, the coating parameters can be set according to actual needs.

[0034] In this embodiment of the invention, the interference principle of the fiber optic FP cavity is multi-beam interference. When a monochromatic plane light wave enters the cavity from one side at a certain angle, it will undergo reflection and transmission. The amplitude and intensity are divided multiple times, forming multiple parallel reflected and transmitted beams, such as... Figure 6 The diagram shows the optical path of a beam propagating in a fiber optic FP cavity. For both reflected and transmitted light, each beam has a fixed optical path difference and phase difference compared to the previous beam. When this fixed optical path difference reaches an integer multiple of the wavelength (or an integer multiple of the phase difference of 2π), transmission produces an intensity maxima, and reflection produces an intensity minima; this is the interference effect of the FP cavity. Figure 6 As shown, the distance between the two end faces P1 and P2 of the optical fiber is d, and the refractive index of the medium between them is n. When monochromatic light enters P1 at a certain incident angle θ0, multiple reflections and transmissions will occur between P1 and P2. Thus, multi-beam interference is completed on the P1 side (reflected light A1, A2, A3, A4, A5) and the P2 side (transmitted light B1, B2, B3, B4).

[0035] In this embodiment of the invention, diffraction is not considered. It is assumed that the two optical fibers are exactly the same, that is, the reflection coefficients of the two end faces are r1=r2=R, and the refractive index of the cavity medium of the fiber FP cavity is n. Then the power transmission coefficient PT of the fiber FP cavity is:

[0036]

[0037] In the above formula, L is the cavity length and λ is the incident light wavelength. When R takes values ​​of 0.04, 0.5, and 0.9 respectively, the refractive index n of the medium and the cavity length L are constants. The power transmission coefficient varies with the incident light wavelength λ as follows: Figure 7As shown (different colors are used to represent different elements in the figure).

[0038] Depend on Figure 7 It can be seen that, by utilizing the characteristic that the wavelength of the FP cavity is related to the optical power transmission coefficient, the fiber optic FP cavity can be used as a periodic bandpass filter, which has the function of wavelength selection.

[0039] The power reflection coefficient PR is:

[0040]

[0041] It is generally believed that once a semiconductor laser reaches a stable state, its output power and frequency remain constant. However, in reality, the randomness of spontaneous emission causes fluctuations in the phase of the light field, resulting in a certain spectral linewidth in the output laser, while continuously altering the intensity and phase of the light field. The fluctuations in laser output intensity manifest as intensity modulation noise, while the phase fluctuations manifest as frequency modulation noise. In this embodiment of the invention, due to the wavelength selection of the fiber optic FP cavity and the external cavity feedback of the reflected light, the intermodal gain and loss difference between multiple longitudinal modes of the semiconductor laser change. This causes the originally average broadened laser gain spectrum to rapidly saturate, enhancing the suppression of similar modes by the preferred oscillating mode, ultimately resulting in a narrow-band laser output. This reduces the intensity and phase noise of the semiconductor laser source, thereby making the energy output of the semiconductor laser source pigtail more stable, significantly reducing the noise in the fiber scanning display image, and improving clarity and stability.

[0042] like Figure 8 The diagram shown is a schematic of a laser light source in an embodiment of the present invention. The light source includes an R, G, and B three-color laser, which can be a laser diode, such as... Figure 8 The red laser diode 80, green laser diode 81 and blue laser diode 82 emit light that is combined into a single beam by an RGB combiner 83, and then coupled into an optical fiber by an optical fiber coupler 84 to form a pigtail light source.

[0043] In this embodiment of the invention, by placing the fiber optic FP cavity on the fiber optic link between the pigtail light source and the fiber optic scanning system, no changes to the pigtail light source and the fiber optic scanning system are required, reducing the complexity of system integration. By controlling the cavity length of the fiber optic FP cavity and the coating parameters of the fiber end face, the display of RGB three-color images can be improved simultaneously. The introduction of the fiber optic FP cavity greatly enhances the anti-interference capability of the pigtail light source and reduces the requirements for controlling stray light. The fiber optic FP cavity can also lower the threshold of the semiconductor laser light source, reducing power consumption; and by controlling the coating parameters of the fiber end face and the cavity length of the fiber optic FP cavity, fiber connection loss can be controlled.

[0044] Based on the same inventive concept, embodiments of the present invention also provide a head-mounted display device employing the aforementioned projection display module, comprising a main body worn on a user's head, wherein at least one of the projection display modules is disposed on the main body. The main body can be implemented as an eyeglass frame or a helmet.

[0045] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0046] Any feature disclosed in this specification (including any appended claims, abstract, and drawings) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0047] This invention is not limited to the specific embodiments described above. The invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A projection display module, comprising: The application relates to a projection display module. The application relates to a projection display module. The application relates to a projection display module. The application relates to a projection display module.

2. The projection display module of claim 1, wherein the light source is a laser diode. The application relates to a projection display module.

3. The projection display module of claim 1, wherein the light source is a laser diode. The application relates to a projection display module.

4. The projection display module of claim 1, wherein the light source is a laser diode. The application relates to a projection display module.

5. The projection display module of claim 3 or 4, wherein the light source is a laser diode. The application relates to a projection display module.

6. The projection display module of claim 3 or 4, wherein the light source is a laser diode. The application relates to a projection display module.

7. The projection display module of claim 1, wherein the light source is a laser diode. The application relates to a projection display module.

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